This invention relates to a synthetic liquid control standard for use in the quality assurance of blood gas instrumentation systems.
The determination of blood pH, pCO.sub.2 and pO.sub.2 is an established diagnostic procedure which is used in conjunction with certain medical and surgical treatments. It is important to know the condition of the patient's circulating blood in terms of its acid-base balance, electrolytes and blood gas levels at all times during such procedures.
Various instrumentation systems have been developed for the determination of the parameters which comprise the blood gases and acid-base balance. These instrumentation systems generally are capable of measuring blood pH, pCO.sub.2 and pO.sub.2. Illustrative of such instrumentation systems are those described in U.S. Pat. Nos. 3,658,478; 3,652,843; 3,763,422; 3,654,445; and 3,874,850. Commercially available instrumentation systems are the Corning 175 Automatic pH/Blood Gas System; the ABL1 Acid-Base Laboratory of the London Company, Radiometer Copenhagen; the IL 113 pH/Blood Gas Analyzer from Instrumentation Laboratory; and the Technicon BGII pH/Blood Gas System.
It is common practice to employ control solutions for verifying the accuracy and reliability of these instrumentation systems. Illustrative of these control solutions for use in blood gas determination systems are the blood gas control standards described in U.S. Pat. Nos. 3,973,913 and 4,126,575. These compositions contain stabilized red blood cells in a buffered solution of bicarbonate ions with an appropriate gaseous head space packaged in a sealed receptacle.
Another typical blood gas control is disclosed in U.S. Pat. No. 4,001,142. This control standard comprises an aqueous solution of a dye, buffering agent, a lower alkyl acid such as acetic acid, triethanolamine, bicarbonate ions and dissolved gases. A variation of this type of blood gas control, described in German Offenlegungsshrift No. 2,727,140 and U.S. Pat. No. 4,163,734, comprises an aqueous solution which contains buffer and a dye (Ponceau 4R) emulsified with perfluorotributlyamine and has dissolved gases in equilibrium therewith.
The blood gas instrumentation systems of the current state of the art generally employ electrodes for measuring pH, pCO.sub.2 and pO.sub.2. For example, the hydrogen ion concentration may be monitored with a pH responsive glass electrode in cooperation with a Ag/AgCl reference electrode; the partial pressure of carbon dioxide (pCO.sub.2) may be sensed in the circulating fluid with a pCO.sub.2 electrode and the partial pressure of oxygen (pO.sub.2) may be similarly monitored with an oxygen-sensing electrode. These gas sensing electrodes will be adapted with a selectively permeable membrane over the tip to permit passage of the relevant gas to be sensed. These membranes may be comprised of materials such as silicone rubber, Teflon.RTM. plastic and the like semi-permeable materials which are permeable to gas but impermeable to liquid.
In actual practice over a period of time, there is a tendency of protein material from the blood samples applied to the blood gas measuring instrument to accumulate on the electrode membrane and thereby plug up the pores of the semi-permeable membrane material or otherwise contaminate the instrument tubing. The present inventors have now developed a completely synthetic liquid control standard for use in blood gas instrumentation systems which provides adequate blood gas control and at the same time promotes the clearing off of protein material from the electrode membrane and tubing system.